1. Field of the Invention
The present invention relates to a technique of embedding information in a document image.
2. Description of the Related Art
There is proposed a technique of embedding information in a document image by changing the spacing between words or characters (Japanese Patent Laid-Open No. 9-186603 and Japanese Patent No. 3728209). This technique represents 1-bit information using two spacings, before and after a character.
However, according to the method of embedding information by using the difference between character spacings, it is difficult to determine whether information is embedded for a proportional font, single-byte character, and the like for which the character spacing is originally narrow. In addition, information may be erroneously extracted owing to noise or distortion generated in printing or scanning.